The invention relates to the field of recording tape transport mechanisms and more particularly to means for supporting, positioning and adjusting the tape in relation to the tape head.
Magnetic tape storage systems are widely used in computer systems for storing and retrieving large amounts of data. A typical system will be described, but the following description should not be taken to encompass the variety of systems available. Current systems typically read and write from parallel tracks on the tape which vary in number based on the design of the system. Each track of the head has a read and a write magnetic transducer (head) arranged in tandem so that the data written by the write head can be verified by the read head. The head pairs may be alternated so that one set of the tracks are written and read when the tape travels in the one direction and the other set is used when the tape is moving in the opposite direction.
Some tapes are written with magnetic servo information thereon to allow positioning the heads in relation to the tracks. All tapes have a magnetic noise floor which is present even when the tape is erased. Therefore, even a tape with no data recorded thereon will generate a noise signal in the read heads and tapes with servo information will also generate signals corresponding to servo information.
For high density recording the tape must be precisely positioned and tensioned as it moves across the head assembly. The tape is typically supported and positioned by support surfaces, for example cylindrical rollers or posts or guides disposed on each side of the head. The support surfaces are positioned behind the head to form the wrap angles which are the angles of the plane of the tape with respect to the air bearing surfaces of the head. Precise wrap angles are necessary for optimum performance.
U.S. Pat. No. 3,123,811 (Mutziger) describes a tape system which has pairs of physically separate heads disposed in a confronting position. The tape is directed through a capstan and pinch roller combination and sequentially over the first pair of heads. The tape then loops around a roller in 180 degree turn and passes sequentially over the second pair of heads. The problem being addressed by Mutziger is that there is a need to synchronize the signals read by the first pair of heads with the signals from the second pair of heads. One source of error in the described system is, of course, in the precise placement of the heads. Mutziger solves the problem by positioning an eccentrically mounted tape guide between the head pairs. The tape travel between the heads in the first pair is straight. The eccentric tape guide is used to deflect and, thereby, lengthen the tape path between the heads in the second pair. The eccentric tape guide is rotated to adjust the precise length of the tape between the second pair of heads to synchronize signals being read from tape. After desired adjustment is obtained, the eccentric tape guide is locked in place to prevent rotation.
Components and methods which increase the precision of the wrap angle are needed in the art.
The invention includes a method for adjusting tape wrap angles and a tape recording and/or reading system with a mechanism allowing adjustment of the wrap angles. The invention applies to heads including single bump and multibump heads. The specific method for adjusting a tape wrap angle depends on how the tape wraps the head. If as is typical for a two or multibump head, the tape wrap angles on the interior edges are fixed during head assembly, then the adjustment is performed for the outside edges. In this case the method for adjusting the outside tape wrap angle comprises the steps of monitoring a signal generated when tape is transported across the head assembly under test from support towards head, reducing the tape wrap angle on the outside edge until the signal from the tape head vanishes, then increasing the wrap angle by moving the tape support a fixed amount, such as might be determined mathematically using the point at which the signal vanishes. Alternatively, in some cases it is possible to adjust the wrap angle until the desired angle is achieved as measured by the signal from the head. Another method is to first adjust the tape wrap angle to nearly zero on both sides of the head using the above method. In fact some head assemblies may even be constructed so that the wrap angle is zero on one side. Then the exterior tape wrap angle can be adjusted by monitoring the signal with tape moving from the guide towards the head, as above, but now it is possible to use in the wrap angle calculation either the point at which signal is lost, or the point at which signal is recovered, as both are well defined and repeatable for a flat contour head. For cylindrical or convex heads when both sides of the module under test are wrapped, the procedure consists in moving tape from module under test towards the guide and unwrapping the tape until the signal first reaches a peak then diminishes. This point can then be used to calculate the optimum wrap angle. The tape system of the invention, preferably includes an adjustment mechanism located on each side (tape-in and tape-out) of the tape head. The adjustment mechanism comprises at least one roller or guide mounted on an adjustable shaft with an eccentric or axially offset portion supporting the roller or guide. The angular orientation of the eccentric shaft is adjustable, thereby allowing precise adjustment of the position of the roller with respect to the tape head assembly. Rotating the shaft moves the eccentric portion of the shaft further behind or closer to the plane of the surface of the head assembly and, therefore, causes the roller or guide mounted on the eccentric portion of the shaft to move similarly, resulting in a change in the corresponding wrap angle of the tape in relation to the head assembly. When the desired wrap angle is achieved, the shaft should be restrained from further rotation by an appropriate friction or other locking means. Although the invention can be used with any type of tape head assembly, it is used to particular advantage with a flat contour tape recording head assembly. The invention provides a means for precisely adjusting the critical wrap angles between tape and head in situ, using signals off the tape itself. One advantage is greater control of wrap angle than is presently obtained. This leads to improved tolerance, which in turn allows the wrap angle to be adjusted to a lower value. Lower wrap angles result in less head and tape wear. Another advantage of the invention is that it eliminates the need to rely on mechanical gauges, etc., and so improves quality assurance. A method of adjusting a wrap angle in a tape system having a roller or guide position adjustment includes optionally setting the roller in a selected initial position then operating the tape system to generate an electrical signal in the head when the tape moves over the rollers and across the head assembly. The signal is monitored while the roller or guide is adjusted (preferably one at a time). There are numerous ways that the signal might be used in the adjustment process depending in part on the type of head and the electronics of the tape system. In either method of adjustment the signal generated by the tape running over the head is monitored to find the angle at which a sharp dropout of the signal when the wrap angle is being reduced or a reappearance of the signal if the angle is being increased. In either case this establishes a critical point (or trigger point) from which the correct adjustment position is determined. Once the desired wrap angle is achieved the shaft should be prevented from further rotation if necessary by an appropriate means, for example, tightening set screws, applying adhesives, etc. Preferably the system allows the wrap angle on each side of the head to be adjusted independently.